Smoke detector plan symbol

A circle marked S on a ceiling position.

Also known as: Smoke alarm plan symbol, Detector head symbol

Engineering & technicalQuiet profile

Meanings

On a building services plan a smoke detector is drawn as a circle at a ceiling position, marked to distinguish it from a heat detector.

Common modern usageVerified fact
Denotes a smoke detector head at the position drawn.
Contexts: Technical drawing
Common modern usageVerified fact
Is distinguished from a heat detector by its marking, the two suiting different rooms: a smoke detector in a kitchen would sound on cooking.
Contexts: Technical drawing

A circle drawn at a ceiling position containing a letter or a small internal mark identifying the detector type.

A fuller structured visual breakdown is not yet documented for this symbol.

IdentityModerate confidence: Moderate confidence because the identity is documented in encyclopedic references, but only a single source has been found so far.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useModerate confidence: Moderate confidence because the current use is documented in encyclopedic references, but only a single source has been found so far.
Visual matchModerate confidence: Moderate confidence because the visual match is documented in encyclopedic references, but only a single source has been found so far.

Architectural drawing
Wikipedia · retrieved 2026-08-24
Tertiary reference. Used for how a plan symbol is drawn and the plain-language name it carries. Not used for any regulatory requirement; building regulations differ by jurisdiction and no record asserts one.

Last reviewed 2026-08-24

Meanings

On a building services plan a smoke detector is drawn as a circle at a ceiling position, marked to distinguish it from a heat detector.

Common modern usageVerified fact

Denotes a smoke detector head at the position drawn.

Common modern usageVerified fact

Is distinguished from a heat detector by its marking, the two suiting different rooms: a smoke detector in a kitchen would sound on cooking.

Confidence

IdentityModerate confidence: Moderate confidence because the identity is documented in encyclopedic references, but only a single source has been found so far.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useModerate confidence: Moderate confidence because the current use is documented in encyclopedic references, but only a single source has been found so far.
Visual matchModerate confidence: Moderate confidence because the visual match is documented in encyclopedic references, but only a single source has been found so far.